Plasmaless dry contact cleaning method using interhalogen compounds

ABSTRACT

A method of removing an oxide layer from an article. The article is located in a reaction chamber. An interhalogen compound reactive with the oxide layer is introduced into the reaction chamber. The interhalogen compound forms volatile by-product gases upon reaction with the oxide layer. For compounds that form volatile chlorides, bromides or iodides, a reducing gas, such as for example hydrogen, ammonia, amines, phosphine, silanes, and higher silanes, may optionally be added simultaneously with the interhalogen to form a volatile by-product. Unreacted interhalogen compound and volatile by-product gases are removed from the reaction chamber. In one embodiment, the temperature in the reaction chamber may be elevated prior to or after introducing the interhalogen compound. In another embodiment, a metal layer is deposited in-situ on a portion of the article within the reaction chamber.

FIELD OF THE INVENTION

The present invention relates to the use of interhalogen compounds toclean substrates to remove or prevent the formation of oxides, and inparticular, the use of interhalogen compounds to clean contacts in-situprior to metal deposition on silicon wafers.

BACKGROUND OF THE INVENTION

Reactive ion etching is a process whereby a low pressure gas is subjectto a radio frequency electric field in a reaction chamber to form aplasma. A plasma is a gas which contains positive, negative and neutralatoms, and/or molecules including radicals and a "gas" of emittedphotons. The ions and radicals in the plasma that form the etchants areaccelerated by an electric field against the material to be etched. Theions/radicals interact with the surface of the atoms or molecules withinthe material to be etched, forming a volatile by-product which issubsequently removed from the reaction chamber.

If a chemically inert gas, such as argon, is ionized and accelerated toimpinge on a substrate surface, material can be removed from the surfaceof the substrate by momentum transfer, a process similar to sandblasting. This process is used in three distinct modes: sputter etching,ion-beam milling and focused ion beam etching. Sputter etching andbroad-ion beam milling use high-energy, inert gas ions (typically Ar⁺)to dislodge material from the substrate surface, a highly anisotropicetch process. Anisotropic etching occurs when the etch rate isconsiderably greater in one direction then in another (also known asunidirectional etching). Isotropic etch refers to etching in alldirections at a relatively even rate.

The inherent poor selectivity and slow etch rate of these purelyphysical processes, however, severely limit their use in the cleaning ofsub-micron patterns. It can be difficult to focus plasma to the bottomof high aspect ratio (depth:width) features. The anisotropic nature ofdry etching makes it difficult to clean two or more surfaces. Forexample, it is often desirable to clean the bottom and side walls of ahigh aspect ratio feature on a substrate. Plasma reactors are difficultto modify to perform both the etching process and metal deposition.Finally, the sputtered material is typically non-volatile and tends tore-deposit onto the substrate and elsewhere in the system.

The ion bombardment in reactive ion etching can also result in a chargebuild-up on insulated surfaces, resulting in damage to the underlyingfilm and semiconductor surface exposed to ion bombardment. For example,if the beam strikes a conducting grounded surface, sufficient secondaryelectrons are generated to balance the space charge of the beam andexternal neutralization is not necessary. If ions impinge on aninsulated surface, however, positive charge can build-up on the surface,damaging the underlying insulator and semiconductor surface. Whenaccumulated surface charge causes excessive current to pass through aninsulator, the damage to the dielectric can be permanent.

Wet process cleaning to remove native oxides is limited in that thesurface tension of the liquid inhibits penetration down into surfacefeatures with small lateral dimensions or high aspect ratios. Wetprocess cleaning is difficult to control. Finally, it is difficult tointegrate wet process cleaning in the same equipment with metaldeposition.

SUMMARY OF THE INVENTION

The present invention is directed to the use of interhalogen compoundsto perform cleaning of a substrate to remove or prevent the formation ofoxide layers. The oxide layer may be a native oxide layer or some otheroxide. The present invention is particularly useful in cleaning highaspect ratio surface features on substrates. The present invention isalso directed to the use of interhalogen compounds to clean contactsin-situ prior to metal deposition of silicon wafers.

One embodiment of the method of the present invention is directed toremoving an oxide layer from at least one surface feature on an article.The article is located in a reaction chamber. An interhalogen compoundreactive with the oxide layer is introduced into the reaction chamber.The interhalogen compound forms by-product gases upon reaction with theoxide layer. Unreacted interhalogen compound and by-product gases areremoved from the reaction chamber.

A photoresistive layer impervious to the interhalogen compound mayoptionally be deposited on a portion of the article to selectively cleanthe article. One or more surface of the surface feature may be cleanedusing the method of the present invention.

In one embodiment, the temperature in the reaction chamber is elevatedduring or after introduction of the interhalogen compound. In anotherembodiment, a metal layer is deposited in-situ on a portion of thearticle within the reaction chamber. In yet another embodiment, thereaction chamber comprises a chemical vapor deposition reaction chamber.

The interhalogen compound is selected from a group consisting of ClF₃,BrF₃, ClF₅, IF₅, IF₇, ClF, BrCl, IBr, ICl, and BrF. In one embodiment,the interhalogen compound is preferably a complex interhalogen gas.Alternatively, the interhalogen compound may be a liquid or solid atroom temperature. Non-fluorine-containing interhalogen may also be used.For compounds that form volatile chlorides, bromides or iodides, areducing gas, such as for example hydrogen, ammonia, amines, phosphine,silanes; and higher silanes, may optionally be added simultaneously withthe interhalogen to form a volatile by-product.

The article may be a silicon wafer or a non-silicon metal or metalloidsubstrate. The surface feature having one or more lateral dimensions ofless than 2 micrometers, or alternatively, less than 0.5 micrometers maybe cleaned using the present method. The surface feature may have anaspect ratio of at least 1:1, although it will be understood surfacefeatures with aspect ratios greater than 40:1 may be cleaned with thepresent method.

The present invention is also directed to a method of in-situ removal ofan oxide layer from a silicon wafer in a chemical vapor depositionchamber prior to metal deposition. Specifically, the method of in-situremoval of an oxide layer from a silicon wafer in a chemical vapordeposition chamber prior to metal deposition, comprises the steps of:locating the silicon wafer in a reaction chamber; introducing aninterhalogen compound reactive with the oxide layer into the reactionchamber, the interhalogen compound forming by-product gases uponreaction with the oxide layer; evacuating unreacted interhalogencompound and by-product gases from the reaction chamber; and depositinga metal layer on a portion of the article within the reaction chamber.

The method of the present invention can also be used to remove an oxidelayer from an article that may not have a surface feature as describedherein. This method can use either a non-fluorine-containinginterhalogen compound reactive with the oxide layer and/or an articlehaving a non-silicon surface.

As used in this application:

"Complex interhalogen" refers to non-diatomic interhalogens, such astetra-atomic, hexa-atomic and octa-atomic interhalogens;

"Lateral dimension" refers to a dimension measured generally parallel tothe surface of the substrate, such as width and diameter of a surfacefeature; and

"Surface features" refers to a trench, via, hole, depression or otherdeviations from a planar surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a generic reactor forchemical-vapor deposition (CVD) suitable for use with the presentin-situ cleaning of contacts prior to metal deposition;

FIG. 2 is a schematic illustration of a pair of adjacent high aspectratio contacts being cleaned showing the diffusion of reactant gasesinto the trench and the diffusion of by-product molecules out of thetrench; and

FIG. 3 is a schematic illustration of a substrate surface beingselectively cleaned.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention is directed to the use of interhalogen compoundsto remove oxide layers prior to metal deposition. The cleaning mayinvolve selective removal of materials, such as at a contact, orcleaning of the entire substrate without patterning, as will bediscussed below. The cleaning is preferably performed in-situ beforemetal deposition so as to prevent the formation of native oxides at thecontact interface. Alternatively, reformation of the oxide layer can beprevented by storing the cleaned substrates in argon or some other inertgas or transferring the substrates directly from the cleaning locationto the metal film deposition location via automated material handlingequipment.

FIG. 1 illustrates a generic reactor 10 suitable for use with thepresent in-situ cleaning of contacts prior to metal deposition. Acombination substrate chuck and heater 12 is located beneath a gasdistribution shower head 14 within a reaction chamber 16. Theinterhalogen compounds are introduced through the inlets 18, which arepreferably gas inlets. Reaction by-products are drawn from the reactionchamber 16 through a vent 22 by a vacuum pump (not shown). The substrate24 is located on the chuck 12 in the reaction chamber 16. The insidesurface of the reaction chamber 16 may be constructed of steel tominimize reaction with the interhalogen compounds. The chemical-vapordeposition gas is typically introduced through gas inlet 20.

An interhalogen gas or vapor from a high vapor pressure liquid may beintroduced into the inlet 18, or by other suitable means, to performin-situ cleaning of substrate 24 prior to metal deposition. The reactionchamber is preferably heated to a temperature of about -20° C. to about700° C. for a period of about 10 seconds to about 10 minutes. Pressureis preferably maintained within the reaction chamber 16 at about 0.0133Pa to about 101,325 Pa. It will be understood that the optimumtemperature and pressure are a function of the interhalogen and theoxide being cleaned. The interhalogen compound may be removed from orflushed-out of the reaction chamber through the vent 22 by introductionof an inert gas at the inlet 18, such as argon. The argon also serves toprevent the formation of native oxides on the substrate 24 prior tometal deposition. After cleaning, CVD may be performed in the reactionchamber 16 without removal or handling of the substrate 24. It will beunderstood that the present in-situ cleaning of contacts usinginterhalogen compounds may be performed in a variety of reactors,including barrel reactors and vertical reactors.

The substrate 24 is typically a silicon wafer containing a layer ofborophosphosilicate glass (BPSG). It will be understood, however, thatthe substrate 24 may be a silicon-containing material or a non-siliconcontaining metal or metalloid material.

Interhalogen compounds generally exist in four stoichiometries: XY, XY₃,XY₅ and XY₇ where X is the heavier halogen. A few ternary compounds arealso known, such as IFCl₂ and IF₂ Cl. For the hexatomic series, only thefluorides are known. The interhalogen compounds suitable for use in thepresent invention include without limit ClF, BrCl, IBr, ICl, BrF, ClF₃,BrF₃, ClF₅, BrF₅, and IF₅.

For use in the present invention, interhalogens that are either gases orhigh vapor pressure liquids at room temperature are preferred due toease of delivery into the reaction chamber. It is also possible to useinterhalogens in solid form at room temperature by heating to the pointof sublimation prior to or after introduction into the reaction chamber.Interhalogens that are solids at room temperature include, for example,IF₇, ICl, and IBr. For example, it is possible to heat the interhalogenprior to delivery into the reaction chamber and maintain an elevatedtemperature using the heating element in the chuck 12 or other suitablemethods. Table 1 summarizes the boiling point and melting point in ° C.of selected interhalogens.

                  TABLE 1    ______________________________________    Property           ClF.sub.3                   BrF.sub.3                          IF.sub.3 ***                                 ClF.sub.5                                      BrF.sub.5                                            IF.sub.5                                                 IF.sub.7    ______________________________________    MP/°C.           -76.3   8.8    --     -103 -60.5 9.4  6.5*    BP/°C.           11.8    125.8  --     -13.1                                      41.3  104.5                                                 4.8**    ______________________________________     *triple point     **Sublimes at 1 atm     ***IF.sub.3 is a yellow solid at room temperature

Metal or metalloid species may be cleaned using the present interhalogencleaning method as long as the resultant metal or metalloid halide formsa gas. Typically, this excludes alkali metals and alkaline earth metalsof the Periodic Table. Suitable metals and metalloids include transitionmetals, i.e., those elements in the Periodic Table with their outermostelectrons in "d" orbitals; lanthanides and actinides, i.e., thoseelements in the Periodic Table with their outermost electrons in "f "orbitals; the heavier elements of Group IIIA, i.e., Group 13 (Al, Ga,In, Ti); the heavier elements of Group IVA, i.e., Group 14 (Sn, Pb); theheavier elements of Group VA, i.e., Group 15 (Bi), and the metalloids(B, Si, Ge, As, Sb, Te).

Interhalogens are useful in removing metal oxides that readily form avolatile halide in the presence of a interhalogen. Although fluorinebased interhalogens are preferred, the interhalogen is generally matchedwith the metal or metalloid being cleaned to provide a volatile product.In particular, fluorine containing interhalogens may or may not producea volatile product upon reacting with certain oxide layers.

Some interhalogen compounds do not form volatile fluorides, but formvolatile chlorides, bromides or iodides, such as aluminum or titaniumhalides. For example, non-fluorine containing interhalogens such as IClmay be used in combination with hydrogen or some other reducing gas toform volatile metal halides, such as titanium chloride or aluminumchloride. Examples of native oxides that can be removed usingnon-fluorine containing interhalogens, with or without hydrogen or someother reducing gas, include silicon dioxide, aluminum oxide and titaniumoxide. Possible reducing gases include hydrogen, ammonia, amines,phosphine, silanes; and higher silanes.

The by-products are typically in gaseous form and are easily removedfrom the vent 22 of the reaction chamber 16 by introducing additionalinterhalogen compounds or an inert gas. The by-products typicallyinclude metal fluorides or chlorides, bromides, iodides, main groupfluorides, chlorides, bromides or iodides, organofluorides, chloridesbromides or iodides and diatomic halogens. The gaseous nature of theby-products facilitates removal from the reaction chamber, asillustrated in FIG. 2.

FIG. 2 illustrates a high aspect ratio trench 30 in aborophosphosilicate glass (BPSG) layer 31 on a silicon substrate 34having an opening 32. The trench 30 has a width or diameter "W" and adepth "D", yielding an aspect ratio of D:W. Width and diameter arecollectively referred to herein as the lateral dimension. An adjacenttrench 30' is located a distance "S" from the trench 30. A doped siliconregion 36 at bottom 37 of the trench 30 is covered by a native oxidelayer 38 of silicon dioxide.

Interhalogen compound 40 reacts with the silicon dioxide 38 along thebottom 37 of the trench 30. The diffusion of the interhalogen compound40 is thermally random but a net diffusion is downward into the trench30 as indicated by downward arrows 42. The by-product molecules 44 areindicated by the circles. The diffusion of the by-product molecules 44is thermally random but a net diffusion is upward through the opening 32of the trench 30 as indicated by upward arrows 46. The concentration ofthe interhalogen compound 40 and the by-product molecules 44 varies withthe aspect ratio of the trench 30. In general, the interhalogen compound40 is more concentrated at shallow depths close to the surface 48 of theBPSG layer 31, and become less concentrated toward the bottom 37. Thepresent method is isotropic in nature and is therefore useful incleaning multiple surfaces simultaneously, such as the bottom 37 andside walls 39 of a trench 30, where appropriate.

High aspect ratio surface features, such as trench 30, typically fall inthe range of about 1:1 to about 5:1, and more likely in a range of about1:1 to about 20:1, although it will be understood that aspect ratios inthe range of about 1:1 to about 40:1 are possible. The presentinterhalogen cleaning method is well suited for use in cleaning surfacefeatures having one or more lateral dimensions W of less than about 2microns, although surface features less than about 0.5 micron may becleaned.

FIG. 3 illustrates an alternative embodiment in which a photoresist 50is optionally deposited on a surface 52 to selectively clean portions ofsubstrate 54. The photoresist 50 does not extend into trench 56 so thatthe native oxide layer 58 will be subject to the interhalogen compound.On the other hand, the photoresist 50 extends across trench 58 toprotect contact 60. The photoresist is typically needed only when anexposed layer, such as a metal contact, is exposed. The photoresist istypically a material that is impervious to the interhalogen cleaningprocess. Polymer resins are known to be suitable photoresists for metal,silicon, silicon dioxide, silicon nitride, and other materials.Commercially available photoresists suitable for use with the presentinterhalogen cleaning process include product OCG ARCH2 available fromOCG Micro Electronic Materials, Inc. located in Santa Clara, Calif. andShipley 9549Q and 549Z, available from Shipley Company, Inc. located inMarlborough, Ma.

The present invention has now been described with reference to severalembodiments described herein, particularly with respect to articleshaving surface features. It will be apparent to those skilled in the artthat many changes can be made in the embodiments without departing fromthe scope of the invention. For example, articles having a planarstructure and no surface features can also be cleaned using the methodof the present invention. Thus, the scope of the present inventionshould not be limited to the structures described herein, but only tostructures described by the language of the claims and the equivalentsto those structures.

What is claimed is:
 1. A method of removing a layer of silicon oxidefrom at least a portion of a surface feature provided on an articlecomprising silicon, the method comprising the steps of:locating thearticle having the surface feature in a reaction chamber; introducing aninterhalogen compound reactive with the silicon oxide layer into thereaction chamber so as to remove the silicon oxide layer from theportion of the surface feature, the interhalogen compound formingvolatile by-product gases upon reaction with the silicon oxide layer;increasing a temperature in the reaction chamber during introduction ofthe interhalogen compound; and removing unreacted interhalogen compoundand volatile by-product gases from the reaction chamber.
 2. The methodof claim 1 wherein the temperature is 3within a range of about -20° C.to about 700° C.
 3. The method of claim 1 further including the step ofincreasing a temperature of the interhalogen compound prior tointroducing the interhalogen compound into the reaction chamber.
 4. Themethod of claim 1 wherein a pressure in the reaction chamber is within arange of about 0.0133 Pa to about 101,325 Pa.
 5. The method of claim 1further including the step of coating at least a portion of the articlewith a photoresistive layer impervious to the interhalogen compound. 6.The method of claim 1 further including the step of depositing in-situ ametal layer on a portion of the article within the reaction chamber. 7.The method of claim 1 wherein the reaction chamber comprises a chemicalvapor deposition reaction chamber.
 8. The method of claim 1 wherein thearticle comprises a silicon wafer.
 9. The method of claim 1 wherein theinterhalogen compound is selected from a group consisting of ClF₃, BrF₃,ClF₅, IF₅, IF₇, ClF, BrCl, IBr, ICl and BrF.
 10. The method of claim 1wherein the interhalogen compound comprises an interhalogen gas.
 11. Themethod of claim 10 wherein the interhalogen gas comprises a complexinterhalogen gas.
 12. The method of claim 1 wherein the interhalogencompound comprises a non-fluorine-containing interhalogen compound. 13.The method of claim 1 wherein the interhalogen compound comprises a highvapor pressure liquid at room temperature.
 14. The method of claim 1wherein the interhalogen compound comprises a solid at room temperaturethat sublimes upon heating to generate an interhalogen vapor.
 15. Themethod of claim 1 wherein the surface feature comprises a depressionwith one or more lateral dimensions of less than about 2 micrometers.16. The method of claim 1 wherein the surface feature comprises adepression with one or more lateral dimensions of less than about 0.5micrometer.
 17. The method of claim 1 wherein the surface feature has anaspect ratio comprising at least about 1:1.
 18. The method of claim 1wherein the surface feature has an aspect ratio comprising at leastabout 5:1.
 19. A method of in-situ removal of a silicon oxide layer froma silicon wafer in a chemical vapor deposition chamber prior to metaldeposition, comprising the steps of:locating the silicon wafer in thedeposition chamber; introducing an interhalogen compound reactive withthe silicon oxide layer into the deposition chamber so as to remove thesilicon oxide layer from the silicon wafer; increasing a temperature inthe chamber during introduction of the interhalogen compound; evacuatingunreacted interhalogen compound and volatile by-product gases from thedeposition chamber; and depositing a metal layer on a portion of thearticle within the deposition chamber.
 20. A method of removing an oxidelayer from a portion of a surface feature provided on an article havinga non-silicon surface, comprising the steps of:locating the articlehaving the non-silicon surface and high aspect ratio surface feature ina reaction chamber, the surface feature having a high aspect ratio ofdepth relative to width of between about 1:1 and about 40:1; introducingan interhalogen compound reactive with the oxide layer into the reactionchamber so as to remove the oxide layer from the portion of the surfacefeature, the interhalogen compound forming volatile by-product gasesupon reaction with the oxide layer; increasing a temperature in thechamber during introduction of the interhalogen compound; and evacuatingunreacted interhalogen compound and volatile by-product gases from thereaction chamber.
 21. The method of claim 20 wherein the interhalogencompound comprises a non-fluorine-containing interhalogen compound. 22.The method of claim 19 wherein the silicon wafer includes a surfacefeature having a high aspect ratio of depth relative to width of betweenabout 1:1 and about 40:1.
 23. The method of claim 19 wherein the siliconwafer includes a surface feature having a high aspect ratio of depthrelative to width of between about 2:1 and about 20:1.
 24. The method ofclaim 20 wherein the surface feature comprises a depression with one ormore lateral dimensions of less than about 2 micrometers.
 25. The methodof claim 19 wherein the temperature is within a range of about -20° C.to about 700° C.